Evaluating Trade-Offs between Target Persistence Levels and Numbers of Species Conserved

A focus of conservation planning is to maximize the probability of species persistence, but this may reduce the number of species that can be secured with a limited budget. Using a data set of 700 New Zealand species, we examine the trade-off between providing a high level of persistence for some species and a lower level of persistence for more species. We find that the target persistence level that delivers the highest conservation outcome is a function of the annual budget, such that lower budgets have lower optimal targets. However, it is never optimal to manage species below a 75% probability of persistence. We introduce a prioritization approach that maximizes biodiversity gains based on a flexible persistence target, and demonstrate how strategies with fixed high-persistence targets can be inefficient. We also illustrate the risks in spreading conservation resources too thinly by undertaking low levels of management on more species.